In sound recording, in order to effectively collect target sound, it is necessary to suppress an inputting of surrounding sounds like noises. To collect sound in an arbitrary direction, target sound can be clearly collected using a directivity microphone. In addition, a realistic sensation can be realized through stereo recording with a wide pitch. In the case of IC recorders, a large number of methods which process input signals by two microphones, emphasize sound in an arbitrary direction, or suppress sounds in other directions to collect sound.
For example, according to the technology disclosed in Patent Document 1, it is determined whether or not input sound is in a target direction based on input signals by two microphones closely disposed, corrects a difference in the phase of the two input signals, and emphasizes sound in the target direction. In addition, according to the technology disclosed in Patent Document 2, two input signals are referred to each other, and filtering is sequentially performed using an obtained signal. When this technology is applied to signals input through two microphones, sound in the same phase can be extracted and emphasized. That is, it becomes possible to emphasize sound in a predetermined direction, and to add directivity.